A line from my favorite Christmas hymn, In the Bleak Midwinter, tells of a season when “Earth stood hard as iron, water like a stone; snow had fallen, snow on snow, snow on snow.” Winter is a season of extremes: extreme beauty, extreme hardship, extreme joy or suffering. We fill this season with festivals of brightly colored lights and decorations, solemn religious services, and gathering around those we love and who love us. Humankind and most other animals survive the winter months by wit, force of will, and luck. If you are lucky enough to have a warm, safe home and protective clothing you can make it through the coldest of days with ease and comfort. Non-human animals fend for themselves; or if lucky, share a warm safe home with their human companions and observe the icy world outside through the safety of a window.
What of plants? Many trees and some plants have the ability to withstand subzero temperatures, even for extended periods. Woody plants can survive being coated in ice, even when losing limbs to breakage from the weight of ice or the strong winds of a winter storm. Some of the ways trees and hardy plants survive winter is by flooding their cells with sugars to prevent the cells from freezing, and proteins to inhibit ice from forming within the cells. Other plants allow all above-ground growth to die to ensure that the roots survive. Deciduous plants drop their leaves in autumn (by a process called senescence) thereby completely avoiding the problem of having to protect foliage from freezing during winter months. Many broadleaf evergreens will curl their leaves to help prevent water-loss via the stomata, to allow snow and ice to fall readily from the leaf, and to help prevent cells from freezing. I think it may, also, help prevent sun damage on cold, clear, and sunny days. Conifers coat their needles with a wax-like substance on the epidermis to help alleviate desiccation and protect the cells within, and to allow snow and ice to readily fall from the needles – less weight on the tree overall. Of course, these protections can fail at extreme temperatures; during prolonged periods of deep cold; or from repeated freeze-thaw periods. And, these self-protection methods occur in plants that have evolved to withstand such weather. A plant adapted to warmer climates will not develop protection from temperatures much colder than those of their native habitat, which is why ‘tender’ plants need additional help from the gardener to survive winter weather.
Damage from freezing weather can be readily apparent, as seen in the pictures below, or it may not present until spring. The gardener can help plants weather the season by a variety of methods: storing tender plants in a protected, enclosed area like a shed or garage (or even in the crawl-space under the house); covering the root zone with extra mulch; or wrapping the plant in protective covering such as landscape fabric, bubble wrap, or even blankets and plastic (to keep the covering dry). If tender plants are grown in-ground rather than in containers, situating the plants close to a wall, hedge, or a house will provide extra protection. Sometimes, this is all that’s necessary to ‘winter over’ a plant that otherwise would not survive the season. If tender plants are grown in containers that can not be moved, make sure the plants’ water needs are met before winter arrives as the combination of desiccation and freezing temperatures will kill a plant that otherwise could have survived freezing weather. Also, wrap the container and plant in protective covering, and remove the feet (if possible) from the container and set it directly upon the deck/patio surface.
The pictures below show leaf curl on Viburnum rhytidophyllum and a rhododendron; freeze-burn on a Asplenium scolopendrium, and leaf damage on a primrose and dusty miller. These plants will recover if history repeats itself, and if an extended or deep freeze doesn’t occur in early spring. I am always impressed and surprised by the tenacity of plants – no matter what deep midwinter brings or how climate changes. Most plants will find a way to adapt. Some plants will die, of course, but overall a majority of plants will survive. I have deep faith in our green world – and great faith in its gardeners!